Tropical Rainbelts Still Shifting Global Crops

CHURCHVILLE, VA–Michel Nasibu, of business consultants KPMG/East Africa, warns that global warming has begun to devastate his continent. He writes in AfricaEagle that: “The mother of all troubles has already started rooting her tentacles all over the continent: Global Warming. . . . . Africa is slowly becoming a desert.”

James Taylor of the Heartland Institute, writing at Forbes.com, says “Not so fast.” Taylor notes a 2009 Boston University study that found satellite data showing a long- term shift in the Sahara Desert from dryer to wetter conditions. BBC News, in fact, has reported that, “Satellite images from the last 15 years do seem to show a recovery of vegetation in the southern Sahara.” Taylor also notes correctly that as the Arctic ice has melted, global rainfall has gotten slightly heavier due to more evaporation from the seas.

Both men’s forecasts are wrong, however. What’s really happening is not that the tropical rainbelts that govern Africa’s critical food production are starting or stopping. They’re moving.

I have written often about the natural 1,500-year Dansgaard-Oeschger climate cycle, which brings us a global warming–and then a global cooling–every 15 centuries. Give or take 500 years. Such a lengthy time scale seems almost incomprehensible. Luckily, we now have historical documents that record the Little Ice Age (1300-1850 AD), the Medieval Warming (950-1300 AD), and the Dark Ages (600-950 AD). Paleoclimate evidence from ice cores, fossil pollen, and the sediments at the bottoms of lakes and seas is now extending our knowledge of such climate cycling back at least a million years.

When the Arctic ice melts in a global warming period–as now–the tropical rain belts are drawn roughly 600 miles north. Julian Sachs of the University of Washington told us in “A Shifting Band of Rain,” (Scientific American, March, 2011), that the rain belts are currently about 330 miles north of their location during the depths of the Little Ice Age in 1600. He’s been measuring the stable isotopes of algae (deuterium and hydrogen) in the lake sediments of scattered Pacific islands. Carbon dated, they clearly show the rain belts moving north over time. Sachs predicts they will move even farther north as the planet

continues to warm.

That will obviously mean problems for the tropics, endangering banana crops in Guatemala and stealing the moisture from the coffee crops in Colombia and Indonesia. The Mexican desert can also come to the southern tier of U.S. states.

Africa at the best of times suffers a drought every 30 to 65 years, and when the rainbelts shift they can have awesome impacts. For example, Ghana’s Lake Bosumtwi suffered a 350-year drought during the Little Ice Age!

Ethiopia’s Aksum Empire thrived during the heyday of the Roman Empire. In one of history’s most dramatic rainfall transitions, the tropical rains had moved north about 200 BC to water North Africa–and thus fed Rome on the other side of the Mediterranean for nearly 800 years. As the Roman Warming ended, however, and the Dark Ages began, the rain belts shifted back south to Kenya and Ghana. Both Aksum and the Roman Empire collapsed.

Who will win and who will lose during the Modern Warming? Primitive man could do nothing but try to walk away from the droughts. Modern man can produce extra food where the rains have shifted, and transport the food to people where the rains have left. Only time will tell whether that’s a better strategy than moving the people. But we now have the transport capacity to do either or both.

All of this simply underlines the reality that the earth’s human societies are now vastly more sustainable than their primitive predecessors.